Interference compensation optically synchronized safety detection system for elevator sliding doors

ABSTRACT

A method for detecting interference energy in a sliding door safety system includes the steps of disposing at least one emitter along a first vertical surface, disposing at least one receiver corresponding to the at least one emitter along a second vertical surface, activating the at least one receiver, activating the at least one emitter to emit an energy beam that includes a modulated square wave of a predetermined frequency, sampling an energy intensity received by the activated at least one receiver a predetermined number of times recording each time a received energy intensity to form a plurality of recorded energy intensities, selecting the lowest magnitude one of the plurality of recorded energy intensities to form a lowest recorded energy intensity, comparing the lowest recorded energy intensity to a threshold value and determining a source of the energy intensity to be external when the lowest recorded energy intensity is less than the threshold value.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a method for detecting energyinterference in an optically synchronized safety detection system forsliding elevator doors and compensating for such interference.

(2) Description of Related Art

In optically synchronized elevator detection and safety systems,consisting of separate emitter and receiver arrays, the energy producedby an emitter array is produced in a fixed sequence or pattern, and thereceiver array predictively enables or activates individual receiversaccording to the fixed sequence produced by the emitters. When anactivated receiver detects sufficient energy from the emitter array, a“connect” is logged for the individual beam being sampled (composed ofthe specific emitter and its corresponding receiver). The receiver arraythen disables the currently enabled receiver and activates the nextreceiver in the scanning sequence. This process continues as long asbeams connect. Broken beams (those for which an individual receiver doesnot detect emitted energy within a specified maximum wait time) causethe detection system to signal a door controller to reopen the doors dueto the detection of an obstruction in the path of the closing doors.

A drawback of one such optically synchronized detection system is thepotential presence of various external sources of light energy orelectrical noise which can interfere with the optical andsynchronization, or sync, functionality of the scan. If the energyproduced by these external sources is modulated similarly to the energytransmitted by the door safety system, the external energy can bereceived by the system and interpreted as detection scanning beam energyproduced by the emitter array and cause false indexing of receivers tocheck the next beam in the scan sequence.

Such false indexing causes loss of sync between the emitter array andthe receiver array, resulting in false obstruction detections and falsereversals of the elevator doors. Sources of interference light energyinclude fluorescent lighting systems, strobe lights associated with firealarm systems, and beacons atop emergency vehicles. Sources of external,impulse type, electrical noise include relay type elevator controllersand electromechanical door operators.

What is therefore needed is a safety detection system for sliding doorswhich ensures proper operation of in the presence of impulse typeelectrical noise and light sources, which produce light similar to thatproduced by the safety detection system for scanning purposes.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod for detecting energy interference in an optically synchronizedsafety detection system for sliding elevator doors and compensating forsuch interference.

In accordance with the present invention, a method for detectinginterference energy in a sliding door safety system comprises the stepsof disposing at least one emitter along a first vertical surface,disposing at least one receiver corresponding to the at least oneemitter along a second vertical surface, activating the at least onereceiver, activating the at least one emitter to emit an energy beamcomprising a modulated square wave of a predetermined frequency,sampling an energy intensity received by the activated at least onereceiver a predetermined number of times recording each time a receivedenergy intensity to form a plurality of recorded energy intensities,selecting the lowest magnitude one of the plurality of recorded energyintensities to form a lowest recorded energy intensity, comparing thelowest recorded energy intensity to a threshold value and determining asource of the energy intensity to be external when the lowest recordedenergy intensity is less than the threshold value.

In accordance with the present invention, the aforementioned methodadditionally comprises the steps of performing statistical analysis uponthe plurality of recorded received energy intensities to determine ameasure of consistency amongst the plurality of recorded received energyintensities when the source of the energy intensity has not previouslybeen determined to be external, and determining a source of the energyintensity to be external if the measure of consistency is sufficientlylow.

In accordance with the present invention, the aforementioned methodadditionally comprises the additional steps of modulating the energybeam with a predefined binary code, sampling an energy signal receivedby the activated at least one receiver a predetermined number of timesrecording each time a received energy signal to form a plurality ofrecorded energy signals, and verifying the presence of the predefinedbinary code in at least one of the sampled plurality of recorded energysignals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A diagram of an elevator sliding door system to which the presentinvention is directed.

FIG. 2 A diagram of a modulated square wave for use in the elevatorsliding door system of the present invention.

FIG. 3 A diagram of a modulated binary code square wave for use in theelevator sliding door system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference to FIG. 1 there is illustrated a vertically arrangedarray of emitters 11 located along the right door 21 of an elevatorsliding door system 10 and a matched, vertically arranged, array ofreceivers 17 located along the left door 23 of an elevator sliding doorsystem 10. While illustrated with reference to a plurality of emitters11 and receivers 17 arranged vertically and programmed to emit andreceive a plurality of energy beams in a predefined sequence, thepresent invention is not so limited. Rather, the present invention isbroadly drawn to encompass any and all configurations of emitters andreceivers arranged to perform a safety scan in an environment whereinspurious, external, electromagnetic signals may interfere with emittedenergy beams.

A representation of the energy beam 23 produced by a single activeemitter 15 is shown. In a preferred embodiment, the energy beam 23comprises IR energy. A single active emitter 15 is turned on and areceiver 17 directly across from the emitter is activated to form anactive receiver 13 is turned on and remains on until it detects theenergy beam's 23 signal. After detecting the energy beam 23, the activereceiver 13 is disabled and the next receiver 17 in the scan sequence inactivated to become the active receiver 13 and to receive the energybeam 23.

When the next emitter 11 in the sequence is turned on to become theactive emitter 15, and the light path to the active receiver 13 is notblocked, the received energy beam 23 signal triggers the next receiver17 in the sequence to be activated, and so on. This pattern repeats foreach emitter/receiver pair.

With the present invention, as the area in the path of the closing doorsis scanned for obstructions, techniques are applied which enable thesafety system to discriminate between the pickup of energy produced bythe safety system to detect objects in the entryway, and energy producedby some external source.

In a preferred embodiment of the present invention, each beam is sampledmultiple times in each door scan frame. The sampling is accomplished bymodulating the energy transmitted with a continuous stream of squarewaves, at a specified frequency. Each beam is sampled successively up toa pre-set maximum number of times. The value of the smallest amplitudesample so acquired is the value actually stored and used as the beamintensity for that beam. If, at any time, during the sampling of aparticular beam, no energy is detected, the beam intensity is set tozero. After sampling the pre-set number of times, the stored beamintensity is compared to a predetermined threshold value. If the storedbeam intensity is less than the predetermined threshold value, thepresence of impulse type energy from an external source is confirmed.This is possible because impulse energy is out of phase with thefrequency at which the sampling is performed. As a result, over a numberof samples, at least one sample resulting from impulse energy willexhibit a low magnitude. In this way, impulse type energy from externalsources can be quickly and easily ignored.

In an alternate embodiment of the present invention, each beam issampled multiple times in each door scan frame. The sampling isaccomplished by modulating the energy transmitted with a continuousstream of square waves 21 at a specified frequency as illustrated inFIG. 2. Multiple sampling and impulse rejections is performed asdescribed for the simplest embodiment above. However, if no sample for aparticular beam results in a determination that the energy receivedoriginated external to the detection system, the resulting energysamples acquired for that beam are compared to determine if the detectedenergy represents the pickup of external energy or actual scanningenergy being produced by the detection system.

If the amplitude of the received energy is not consistent, from sampleto sample, the determination is made that the received energy originatedexternal to the safety system and is rejected. If the amplitude of theenergy is consistent, from sample to sample, the determination is madethat the energy was actually scanning energy produced by the detectionsystem. In a preferred embodiment, a maximum amplitude deviation amongstall of the samples is computed and analyzed to determine if the samples,taken as a whole, are sufficiently consistent to confirm that thereceived energy came from the detection system. However, any number offorms of statistical analysis may be performed to determine theconsistency of the samples.

In yet another alternative embodiment of the present invention, eachbeam is sampled multiple times in each door scan frame. The sampling isaccomplished by modulating the energy transmitted with a specific binarycode 31 as illustrated in FIG. 3. As each sample is being acquired, andwhile the amplitude of the sample is being measured, the binary codeexpected to be modulating the received signal is verified. Multiplesampling and impulse rejection is performed, just as described above.However, if no sample for a particular beam results in a “no detect”,the resulting energy samples for that beam, are compared to determine ifthe detected energy represents the pickup of external energy or actualscanning energy being produced by the detection system. If the amplitudeof the received energy is not consistent, from sample to sample, or thebinary modulation code is not verified, the determination is made thatthe received energy originated external to the safety system and isrejected. If the amplitude of the energy is consistent, from sample tosample, or the binary modulation code is verified, the determination ismade that the energy was actually scanning energy produced by thedetection system.

It is apparent that there has been provided in accordance with thepresent invention an optically synchronized safety detection system forsliding elevator doors capable of compensating for interference whichfully satisfies the objects, means, and advantages set forth previouslyherein. While the present invention has been described in the context ofspecific embodiments thereof, other alternatives, modifications, andvariations will become apparent to those skilled in the art having readthe foregoing description. Accordingly, it is intended to embrace thosealternatives, modifications, and variations as fall within the broadscope of the appended claims.

1. A method for detecting interference energy in a sliding door safetysystem comprising the steps of: disposing at least one emitter along afirst vertical surface; disposing at least one receiver corresponding tosaid at least one emitter along a second vertical surface; activatingsaid at least one receiver; activating said at least one emitter to emitan energy beam comprising a modulated square wave of a predeterminedfrequency; sampling an energy intensity received by said activated atleast one receiver a predetermined number of times recording each time areceived energy intensity to form a plurality of recorded energyintensities; selecting the lowest magnitude one of said plurality ofrecorded energy intensities to form a lowest recorded energy intensity;comparing said lowest recorded energy intensity to a threshold value;and determining a source of said energy intensity to be external whensaid lowest recorded energy intensity is less than said threshold value.2. The method of claim 1 comprising the additional steps of: performingstatistical analysis upon said plurality of recorded received energyintensities to determine a measure of consistency amongst said pluralityof recorded received energy intensities when said source of said energyintensity has not previously been determined to be external; anddetermining a source of said energy intensity to be external if saidmeasure of consistency is sufficiently low.
 3. The method of claim 2comprising the additional step of modulating the energy beam with apredefined binary code.
 4. The method of claim 3 comprising theadditional step of: sampling an energy signal received by said activatedat least one receiver a predetermined number of times recording eachtime a received energy signal to form a plurality of recorded energysignals; and verifying the presence of said predefined binary code in atleast one of the sampled plurality of recorded energy signals.
 5. Themethod of claim 1 wherein disposing said at least one emitter along afirst vertical surface comprises disposing said at least one emitteralong an elevator door.
 6. The method of claim 1 wherein disposing saidat least one receiver corresponding to said at least one emitter along asecond vertical surface comprises disposing said at least one receiveralong an elevator door.
 7. The method of claim 1 wherein said energybeam comprises IR energy.